First of all, I love Axcrypt!
It appears that the first 15 bytes of every cyphertext file created with axcrypt are the same. This makes all axcrypt encrypted files easily identifiable with a search (regardless of filename or location) .
What is in this fifteen bytes? Hopefully not the initialization vector? If so, I would think that each file gets a random and unique initialization vector.
Truecrypt (admittedly, a different solution to a different problem) outputs files with no characteristic "signature" so that encrypted data is indistinguishable from random data. That would seem to be a desirable behavior for axcrypt also (for plausible deniability).
I downloaded the source code, but with a quick glance I decided that it would take me forever to find the appropriate section to answer my question.